The present invention relates to a control device for an electric motor drive device including a voltage conversion section that converts a power source voltage from a DC power source to generate a desired system voltage and a DC/AC conversion section that converts the system voltage into an AC voltage to supply the resulting AC voltage to an AC electric motor.
An electric motor drive device that converts a DC voltage from a DC power source into an AC voltage through an inverter to drive an AC electric motor is generally used. As the rotational speed of the electric motor becomes higher, the voltage induced by the electric motor becomes higher. Thus, in order to prevent the induced voltage from exceeding the maximum output voltage of the inverter which hinders the flow of a required current through the electric motor, field weakening control is occasionally performed to weaken the field magnetic flux of the electric motor. When the field weakening control is performed, however, the maximum torque that can be output by the electric motor reduces. In order to address the above issue, International Patent Application Publication No. WO 2003/015254 below describes an electric motor drive device including a voltage boost converter that boosts a power source voltage from a DC power source to expand the maximum torque control region to a higher rotational speed range. International Patent Application Publication No. WO 2003/015254 below also describes the configuration of a control device that calculates an appropriate system voltage command value (inverter input voltage target value) in accordance with the target torque and the rotational speed of the electric motor and controls the voltage boost converter so as to achieve the system voltage command value in order to control the electric motor drive device described above.